Look at the pie chart below.
What do you see? Would you be able to tell the difference between the blue, the red and the green sectors if they weren't labeled and showing numbers behind? I could not.
Why? First, the percentage does not add up to 100%.
Second, the numbers are too similar and the human brain just cannot see the difference of angles that express the volumes. Such data is much easier expressed with bar charts.
See the difference? Now you can see that Palin was actually leading in the presidential run at that moment.
Third, forget the 3D charts. Charts are abstract enough, do not overdo it by adding the third dimension. It is just cruelty to our cognitive abilities.
To conclude, use pie chart only to